This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The purpose of this study is to determine the safety of the prime-boost regimen of priming with CVD 909, a live attenuated Vi+ S. Typhi strain, followed by boosting with licensed parenteral Vi polysaccharide vaccine in healthy adult volunteers. Healthy adult volunteers from the Baltimore community will be recruited for this study. Volunteers will be appropriately screened and will give informed, written consent before study activities begin. Twenty-eight healthy adult outpatient volunteers will be randomized to receive either 5x109 cfu of CVD 909 typhoid vaccine with buffer or buffer placebo alone. Three weeks later, all volunteers will receive 25 ug (0.5 ml) of licensed purified Vi polysaccharide vaccine (Typhim, Sanofi Pasteur, formerly Aventis Pasteur) by the intramuscular route. Blood for serum and ASC responses to Vi, S. Typhi LPS, and O antigen will be drawn before and after the Vi boost.